Bioequivalence and Bioavailability Forum

Hi Cedric,

❝ What is the basis behind the requirement that the LLOQ of the calibration range has to be less than 5% of Cmax?

The cut-off for excluding subjects (“substantial” carry-over from earlier periods in cross-over studies due to a too short wash-out phase) in many guidelines on BE is 5% of C_max.

❝ Is the BE result still valid if the LLOQ is > 5% of Cmax?

≤5% of C_max is the target mentioned in guidelines on bioanalytical method validation. Now the question is: Where to get the value of C_max from? I would suggest to be conservative (i.e., not work with an average reported in the literature) but take between-subject variability into account. Many GLs on BE require ≥80% of AUC_∞ and/or ≥3t_½ to be covered by measured data. There is no simple relationship between the suggested LLOQ and these metrics, but should be seen as a reasonably good starting point. Some drugs are metabolized by enzymes showing genetic polymorphism. Even if you have taken that into account (extensive metabolizers result in a high LLOQ/C_max-ratio) sometimes you face ultra-fast metabolizers… However, in a cross-over study the test/reference-ratio would still be valid.